Artist’s impressions of the TRAPPIST-1 planetary system
Artist’s impressions of the TRAPPIST-1 planetary system
Artist’s impressions of the TRAPPIST-1 planetary system
The ultracool dwarf star TRAPPIST-1 in the constellation of Aquarius
The sizes, masses and temperatures of the seven TRAPPIST-1 planets and others
Properties of the seven TRAPPIST-1 planets compared to other known planets
Properties of the seven TRAPPIST-1 planets
Comparison of the properties of the seven TRAPPIST-1 planets
Comparison of the TRAPPIST-1 system and the Solar System
Videos
ESOcast 150 Light: Planets around TRAPPIST-1 Probably Rich in Water
First glimpse of what Earth-sized exoplanets are made of
A new study has found that the seven
planets orbiting the nearby ultra-cool dwarf star TRAPPIST-1 are all
made mostly of rock, and some could potentially hold more water than
Earth. The planets' densities, now known much more precisely than
before, suggest that some of them could have up to 5 percent of their
mass in the form of water — about 250 times more than Earth's oceans.
The hotter planets closest to their parent star are likely to have dense
steamy atmospheres and the more distant ones probably have icy
surfaces. In terms of size, density and the amount of radiation it
receives from its star, the fourth planet out is the most similar to
Earth. It seems to be the rockiest planet of the seven, and has the
potential to host liquid water.
Planets around the faint red star TRAPPIST-1, just 40 light-years from Earth, were first detected by the TRAPPIST-South telescope at ESO’s La Silla Observatory in 2016. In the following year further observations from ground-based telescopes, including ESO’s Very Large Telescope and NASA’s Spitzer Space Telescope, revealed that there were no fewer than seven planets in the system,
each roughly the same size as the Earth. They are named
TRAPPIST-1b,c,d,e,f,g and h, with increasing distance from the central
star [1].
Further observations have now been made, both from telescopes on the ground, including the nearly-complete SPECULOOS facility at ESO’s Paranal Observatory, and from NASA’s Spitzer Space Telescope and the Kepler Space Telescope.
A team of scientists led by Simon Grimm at the University of Bern in
Switzerland have now applied very complex computer modelling methods to
all the available data and have determined the planets’ densities with
much better precision than was possible before [2].
Simon Grimm explains how the masses are found: "The TRAPPIST-1
planets are so close together that they interfere with each other
gravitationally, so the times when they pass in front of the star shift
slightly. These shifts depend on the planets' masses, their distances
and other orbital parameters. With a computer model, we simulate the
planets' orbits until the calculated transits agree with the observed
values, and hence derive the planetary masses."
Team member Eric Agol comments on the significance: "A goal of
exoplanet studies for some time has been to probe the composition of
planets that are Earth-like in size and temperature. The discovery of
TRAPPIST-1 and the capabilities of ESO’s facilities in Chile and the
NASA Spitzer Space Telescope in orbit have made this possible — giving
us our first glimpse of what Earth-sized exoplanets are made of!"
The measurements of the densities, when combined with models of the
planets’ compositions, strongly suggest that the seven TRAPPIST-1
planets are not barren rocky worlds. They seem to contain significant
amounts of volatile material, probably water [3],
amounting to up to 5% the planet's mass in some cases — a huge amount;
by comparison the Earth has only about 0.02% water by mass!
"Densities, while important clues to the planets' compositions,
do not say anything about habitability. However, our study is an
important step forward as we continue to explore whether these planets
could support life," said Brice-Olivier Demory, co-author at the University of Bern.
TRAPPIST-1b and c, the innermost planets, are likely to have rocky cores and be surrounded by atmospheres much thicker than Earth's. TRAPPIST-1d,
meanwhile, is the lightest of the planets at about 30 percent the mass
of Earth. Scientists are uncertain whether it has a large atmosphere, an
ocean or an ice layer.
Scientists were surprised that TRAPPIST-1e
is the only planet in the system slightly denser than Earth, suggesting
that it may have a denser iron core and that it does not necessarily
have a thick atmosphere, ocean or ice layer. It is mysterious that
TRAPPIST-1e appears to be so much rockier in its composition than the
rest of the planets. In terms of size, density and the amount of
radiation it receives from its star, this is the planet that is most
similar to Earth.
TRAPPIST-1f, g and h are far enough from the host star that water could be frozen into ice across their surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules that we find on Earth, such as carbon dioxide.
"It is interesting that the densest planets are not the ones that are the closest to the star, and that the colder planets cannot harbour thick atmospheres," notes Caroline Dorn, study co-author based at the University of Zurich, Switzerland.
TRAPPIST-1f, g and h are far enough from the host star that water could be frozen into ice across their surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules that we find on Earth, such as carbon dioxide.
"It is interesting that the densest planets are not the ones that are the closest to the star, and that the colder planets cannot harbour thick atmospheres," notes Caroline Dorn, study co-author based at the University of Zurich, Switzerland.
The TRAPPIST-1 system will continue to be a focus for intense
scrutiny in the future with many facilities on the ground and in space,
including ESO’s Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope.
Astronomers are also working hard to search for further planets
around faint red stars like TRAPPIST-1. As team member Michaël Gillon
explains [4]: "This
result highlights the huge interest of exploring nearby ultracool dwarf
stars — like TRAPPIST-1 — for transiting terrestrial planets. This is
exactly the goal of SPECULOOS, our new exoplanet search that is about to
start operations at ESO’s Paranal Observatory in Chile.”
Notes
[1] The planets were discovered using the ground-based TRAPPIST-South at ESO’s La Silla Observatory in Chile; TRAPPIST-North in Morocco; the orbiting NASA Spitzer Space Telescope; ESO’s HAWK-I instrument on the Very Large Telescope at the Paranal Observatory in Chile; the 3.8-metre UKIRT in Hawaii; the 2-metre Liverpool and 4-metre William Herschel telescopes on La Palma in the Canary Islands; and the 1-metre SAAO telescope in South Africa.
[2] Measuring the densities of
exoplanets is not easy. You need to find out both the size of the planet
and its mass. The TRAPPIST-1 planets were found using the transit
method — by searching for small dips in the brightness of the star as a
planet passes across its disc and blocks some light. This gives a good
estimate of the planet’s size. However, measuring a planet’s mass is
harder — if no other effects are present planets with different masses
have the same orbits and there is no direct way to tell them apart. But
there is a way in a multi-planet system — more massive planets disturb
the orbits of the other planets more than lighter ones. This in turn
affects the timing of transits. The team led by Simon Grimm have used
these complicated and very subtle effects to estimate the most likely
masses for all seven planets, based on a large body of timing data and
very sophisticated data analysis and modelling.
[3] The models used also consider
alternative volatiles, such as carbon dioxide. However, they favour
water, as vapour, liquid or ice, as the most likely largest component of
the planets’ surface material as water is the most abundant source of
volatiles for solar abundance protoplanetary discs.
More Information
This research was presented in a paper entitled “The nature of the
TRAPPIST-1 exoplanets”, by S. Grimm et al., to appear in the journal Astronomy & Astrophysics.
The team is composed of Simon L. Grimm (University of Bern, Center
for Space and Habitability, Bern, Switzerland) , Brice-Olivier Demory
(University of Bern, Center for Space and Habitability, Bern,
Switzerland), Michaël Gillon (Space Sciences, Technologies and
Astrophysics Research Institute, Université de Liège, Liège, Belgium),
Caroline Dorn (University of Bern, Center for Space and Habitability,
Bern, Switzerland; University of Zurich, Institute of Computational
Sciences, Zurich, Switzerland), Eric Agol (University of Washington,
Seattle, Washington, USA; NASA Astrobiology Institute’s Virtual
Planetary Laboratory, Seattle, Washington, USA; Institut d’Astrophysique
de Paris, Paris, France), Artem Burdanov (Space Sciences, Technologies
and Astrophysics Research Institute, Université de Liège, Liège,
Belgium), Laetitia Delrez (Cavendish Laboratory, Cambridge, UK; Space
Sciences, Technologies and Astrophysics Research Institute, Université
de Liège, Liège, Belgium), Marko Sestovic (University of Bern, Center
for Space and Habitability, Bern, Switzerland), Amaury H.M.J. Triaud
(Institute of Astronomy, Cambridge, UK; University of Birmingham,
Birmingham, UK), Martin Turbet (Laboratoire de Météorologie Dynamique,
IPSL, Sorbonne Universités, UPMC Univ Paris 06, CNRS, Paris, France),
Émeline Bolmont (Université Paris Diderot, AIM, Sorbonne Paris Cité,
CEA, CNRS, Gif-sur-Yvette, France), Anthony Caldas (Laboratoire
d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, Pessac, France),
Julien de Wit (Department of Earth, Atmospheric and Planetary Sciences,
Massachusetts Institute of Technology, Cambridge, Massachusetts, USA),
Emmanuël Jehin (Space Sciences, Technologies and Astrophysics Research
Institute, Université de Liège, Liège, Belgium), Jérémy Leconte
(Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, Pessac,
France), Sean N. Raymond (Laboratoire d’astrophysique de Bordeaux, Univ.
Bordeaux, CNRS, Pessac, France), Valérie Van Grootel (Space Sciences,
Technologies and Astrophysics Research Institute, Université de Liège,
Liège, Belgium), Adam J. Burgasser (Center for Astrophysics and Space
Science, University of California San Diego, La Jolla, California, USA),
Sean Carey (IPAC, Calif. Inst. of Technology, Pasadena, California,
USA), Daniel Fabrycky (Department of Astronomy and Astrophysics, Univ.
of Chicago, Chicago, Illinois, USA), Kevin Heng (University of Bern,
Center for Space and Habitability, Bern, Switzerland), David M.
Hernandez (Department of Physics and Kavli Institute for Astrophysics
and Space Research, Massachusetts Institute of Technology, Cambridge,
Massachusetts, USA), James G. Ingalls (IPAC, Calif. Inst. of Technology,
Pasadena, California, USA), Susan Lederer (NASA Johnson Space Center,
Houston, Texas, USA), Franck Selsis (Laboratoire d’astrophysique de
Bordeaux, Univ. Bordeaux, CNRS, Pessac, France) and Didier Queloz
(Cavendish Laboratory, Cambridge, UK).
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Links
- Research paper
- Link to Hubble release on atmospheres of TRAPPIST-1 planets
- More information about TRAPPIST-South
- More information about SPECULOOS
- NASA’s Spitzer Space Telescope
- NASA’s Kepler Space Telescope
Contacts
Simon Grimm
SAINT-EX Research Group, University of Bern, Center for Space and Habitability
Bern, Switzerland
Tel: +41 31 631 3995
Email: simon.grimm@csh.unibe.ch
Brice-Olivier Demory
SAINT-EX Research Group, University of Bern, Center for Space and Habitability
Bern, Switzerland
Tel: +41 31 631 5157
Email: brice.demory@csh.unibe.ch
Richard Hook
ESO Public Information Officer
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO/News
